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A-Level Chemistry of alcohols and of phenol
What the A-Level syllabus expects for Chemistry of alcohols and of phenol, and how to practise it.
What the syllabus expects
- Recall alcohol chemistry, taking ethanol as the example:
- combustion
- nucleophilic substitution to a halogenoalkane using a hydrogen halide, HX, or PCl5
- reaction with sodium
- oxidation to a carbonyl compound with acidified K2Cr2O7 and heat under distillation, and to a carboxylic acid from a primary alcohol with acidified KMnO4 or acidified K2Cr2O7 under reflux
- dehydration to an alkene over a concentrated H3PO4 catalyst with heat
- Propose tests that set primary, secondary and tertiary alcohols apart, mild oxidation being one.
- Infer a CH3CH(OH)- group in an alcohol when warm alkaline aqueous iodine converts it to tri-iodomethane.
- Recall phenol chemistry through the following reactions:
- with bases
- with sodium
- brominating the ring with aqueous Br2 to give 2,4,6-tribromophenol, and nitrating it with dilute HNO3 to yield 2-nitrophenol together with 4-nitrophenol
- Explain why water, phenol and ethanol differ in acidity in aqueous medium, reading them as Bronsted-Lowry acids.
How it's examined
Questions on this topic most often ask you to name. About 2% of the past-paper style questions in Rae's bank for this subject sit in this topic.
Worked examples
Example 1 (3 marks)
Reacting an excess of phenol with epichlorohydrin C under basic conditions produces H, whose ¹³C NMR spectrum shows 7 signals. Two further products, J and K, can also be separated out, where K arises from J and J arises from H. phenol + epichlorohydrin C → H [C₉H₁₁ClO₂] + J [C₉H₁₀O₂] + K [C₁₅H₁₆O₃] (base present) Draw the structures of H, J and K.
Show the worked answer
Epichlorohydrin C is 2-(chloromethyl)oxirane (ClCH2-CH(-O-)CH2 epoxide). With phenoxide (base): H [C9H11ClO2]: phenoxide opens the epoxide ring to give 3-chloro-1-phenoxypropan-2-ol, C6H5-O-CH2-CH(OH)-CH2Cl. J [C9H10O2]: intramolecular Williamson - the alkoxide (from the OH) displaces Cl to reform an epoxide, giving glycidyl phenyl ether (2-(phenoxymethyl)oxirane), C6H5-O-CH2-CH(-O-)CH2. (H loses HCl.) K [C15H16O3]: a second phenoxide opens the epoxide of J to give 1,3-diphenoxypropan-2-ol, C6H5-O-CH2-CH(OH)-CH2-O-C6H5. (J + phenol.)
Example 2 (2 marks)
Pentan-1-ol (C₅H₁₁OH) serves as a useful building block in making organic compounds. Provide the structural formula and the name of a different primary alcohol that is an isomer of pentan-1-ol.
Show the worked answer
Pentan-1-ol is C5H12O. A different primary alcohol isomer keeps the -CH2OH group but changes the carbon skeleton, e.g. 3-methylbutan-1-ol: (CH3)2CH-CH2-CH2OH. This is C5H12O with the -OH on a carbon bearing two H's, so it is a primary alcohol.
More A-Level H2 Chemistry topics
The make-up of the atom and how its electrons are arranged · How atoms bond and how that governs a substance's behaviour · Ideal gases and working with gas mixtures · Competing definitions of acids and bases · Trends in the elements across a period and down a group · The mole and reacting-quantity calculations · all of A-Level H2 Chemistry